A light-emitting diode (LED) is a new semiconductor illumination light source, which has become a hot spot of studies in recent years by virtue of the advantages of good energy-saving property, good environmental friendliness, long service life, high light efficiency, etc., and has a wide range of applications in the fields of displays, lighting lamps, indicator lamps, signal lamps, etc. Phosphors for white light LEDs can be divided into three types: a yellow-emitting phosphor which can be excited by a blue LED chip; three-primary-color (red/green/blue) phosphors which can be excited by near ultraviolet light; and a single-phased white-emitting phosphor which can be excited by near ultraviolet light. Here, there are problems of difficulties in color reabsorption and proportion regulation when a near ultraviolet chip is covered with three-primary-color (red/green/blue) phosphors. Although many new systems have been found and reported about the single-phased white-emitting phosphors, such as CaIn2O4:Eu3+, Sr2SiO4:EU2+, Ca9Y(PO4)7:EU2+, Mn2+, etc., the luminescence efficiencies thereof are still relatively low.
White LEDs using blue InGaN chips as an excitation light source have attracted attention due to their advantages of low energy consumption, long service life, small volume, light weight, compact structure, no pollution, good stability, etc. At present, white light can be achieved by blue-yellow mixed light obtained by exciting a yellow-emitting phosphor YAG:Ce3+ using blue InGaN chip as an excitation light. Blue light emitted by the InGaN chip is partly absorbed by the YAG:Ce3+ phosphor and converted to yellow emission with a long wavelength, and the unabsorbed blue light and the yellow light emitted by the YAG:Ce3+ phosphor are recombined to obtain a white light. However, the white light obtained by this method has a relatively low color rendering index and a relatively high color temperature due to the lack of red component in the spectrum, and is a type of cold white light which is not suitable for the fields of indoor illumination, etc.
In order to achieve the warm white light emission, a typical method is adding sulfur-containing red-emitting phosphors such as CaS:Eu2+ and SrS:Eu2+ or nitride red-emitting phosphors such as Sr2Si5N8:Eu2+ to this system. However, the sulfur-containing red-emitting phosphors are sensitive to moisture and instable in chemical and thermal properties. The preparation of nitrides and oxynitrides is difficult and required high nitrogen pressure, and the cost of this kind of product is high. Therefore, it is not advantageous for large-scale industrial production, such that the application of white LEDs is limited.